1. Technical Field of the Invention
The present invention relates to universal motors and, in particular, to a speed controller for a universal motor subject to varying torque loads.
2. Description of Related Art
Universal motors are used in a wide variety of applications because of their low cost and versatility. It is difficult, however, to control the speed of a universal motor when presented with varying torque loads.
Usually, a speed sensor is attached to the motor to provide feedback to some sort of closed loop control circuitry. While this has been done in the past, the additional cost of the sensor and installation on the motor somewhat negate the low cost advantage of the universal motor.
Prior art speed controllers are shown in U.S. Pat. Nos. 4,527,101 and 5,986,417, the disclosures of which are hereby incorporated by reference.